The present invention relates to a vortex flow generator and, more particularly, to a vortex flow generator which is constructed and operated with a minimum amount of error as regards its instrumental function even when there is a change in the velocity of the flow's distribution due to the configuration of the flow's piping.
An inferential type of flow meter is an instrument for determining the quantity of fluid or the velocity of the fluid's flow by measuring the physical quantity of the fluid produced in relation to the fluid's flow. To assure a certain relationship between the fluid's flow and the corresponding physical quantity of the fluid it is necessary to keep a constant state of the fluid's flow to be measured. For this reason, in order to attain the required accuracy of the inferential type of flow meter, it is necessary to provide a flow-rectifying device at the upstream side in the flow pipe wherein the flow meter is installed. Constructions of flow-rectifying devices and piping conditions for orifice and turbine flow meters are defined by the international standard and the national standard.
It is well known that a vortex flow meter is related to an inferential type of flow meter which utilize a number of Karman's vortexes produced by a vortex generator installed in a flow pipe and which is substantially proportional to the flow rate of the fluid within a certain range of Reynolds number. This proportional constant is called the Strouhal number. In an ideal vortex flow meter, the Strouhal number can be kept at a constant value even when the Reynolds number varies. In other words, the ideal vortex flow meter has a constant characteristic (Strouhal number) in a wide range of the fluid's flow and is least affected by the physical properties of a fluid and the conditions of the piping. However, any practical vortex flow meter has a Strouhal number depending on a Reynolds number and its characteristic may be affected by the piping's conditions.
A conventional vortex flow meter has a simple construction where a vortex generator is disposed at a right angle to the axis of the fluid's flow inside a cylindrical body. Many proposals for the shape and quantity of the vortex generators and the internal construction of the vortex flow meter have been made to keep the Strouhal number of the flow meters at a constant value against the Reynolds number. For example, one of the proposals was the improvement of the ratio d/D (width "d" of a vortex generator in perpendicular direction to the fluid's flow and an inside diameter "D" of the body) and a vortex detecting position. Especially, most available vortex flow meters have a ratio d/D being nearly equal to 0.28 in order to aim at obtaining the characteristic satisfying the stable two-dimensional conditions of the ideal Karman's vortex street.
However, any practical vortex flow meter does not detect Karman's vortexes produced by a two-dimensional flow but rather those produced by a three-dimensional flow. Consequently, the characteristic of the vortex flow meter varies depending upon a change in the three-dimensional flow. For example, a bent pipe (including an elbow portion), reducer, diffuser, valve, branch pipe and collector may produce a rotational flow and deflect the flow of the fluid which in turn causes a change in the instrumental error of the vortex flow meter. A flow rectifier is provided to eliminate the above-mentioned irregularity of flow. Components of the rotational flow and the deflected flow may still remain in the flow of the fluid passing through the vortex flow meter, which affects the flow meter's instrumental error.